1. Field of the Invention
The present invention relates to a boot for sealing a universal joint such as a constant velocity universal joint (CVJ) used in a driving shaft or the like of a motor vehicle.
2. Description of Conventional Art
The constant velocity universal joint (CVJ) used in a driving shaft or the like of a motor vehicle is sealed with a boot so as to prevent lubricant grease filled in a joint unit from leaking out thereof and to prevent muddy water and dust from intruding into the joint unit. FIG. 5 is a partially sectional side view showing such a kind of boot for the constant velocity universal joint, and FIG. 6 is a sectional view showing a deformed state of the boot 100 shown in FIG. 5.
The boot 100 shown in FIG. 5 is formed of rubber-like elastic material by blow molding or injection molding, and comprises an flexible bellows member 101 having three mountain portions 101a, 101c and 101e and two valley portions 101b and 101d which extend circumferentially and formed alternately, a large-diameter mounting portion 102 formed at one end of the bellows member 101, and a small-diameter mounting member 103 formed at the other end of the bellows member 101, and the first mountain portion 101a next to the large-diameter mounting potion 102 in the bellows member 101 rises from the large-diameter mounting portion 102 (for example, referring to Japanese unexamined patent publication No. 2003-49944).
The boot 100 is clamped and fixed by a clamping band 104 made of a metal material at the large-diameter mounting member 102 onto an outer periphery of an end of the outer ring 201 formed at the side of one rotation shaft 202 in the constant velocity universal joint 200, and is clamped and fixed by another clamping band 105 made of a metal material at the small-diameter mounting member 103 onto an outer periphery of the other rotation shaft 203 connected in such a manner as to be angularly displaceable with respect to a shaft axis of the outer ring 201 (rotation shaft 202) by a bearing mechanism (not shown) inside the outer ring 201, thereby to prevent foreign materials from entering into the bearing mechanism of the constant velocity universal joint 200, and to prevent lubricant grease filled in the bearing mechanism from leaking out thereof.
Further, since the boot 100 is rotated together with as the outer ring 201 (rotation shaft 202) and rotation shaft 203, when the rotation shaft 203 is in a state of being angularly displaced with respect to the shaft axis of the outer ring 201, the bellows member 101 is deformed in such a repetitious fashion as to be extended in a half rotational cycle, while contracted in another half rotational cycle. Consequently, the above-mentioned bellows member 101 is required to have a sufficient film length for smooth deformation, even when the rotation shaft 203 is angularly displaced largely as shown in FIG. 6. Because if the film length is insufficient, when the rotation shaft 203 is angularly displaced largely, the first mountain portion 101a next to the large-diameter mounting member 102 in the bellows member 101 is reversed to produce a depression A as shown in FIG. 6, resulting in increase in amount of bending deformation. Thus, because of such repetition of reversing, there occurs a problem that the bellows member 101 is deteriorated at the first mountain portion 101a due to fatigue, and its durability is lowered.
Further, it is effective to enlarge the outside diameter of the mountain portion 101a (and mountain portions 101c, 101e) to secure sufficient film length of the bellows member 101 in order to prevent the reversing (depression A). However, in the case where a strict restriction is imposed on the outside diameter from the view point of designing, it has been difficult to secure the sufficient film length.